1. Field of the Invention
This invention relates to a method for midway starting a machining program in a numerical control (NC) system, and more particularly, relates to a method for starting the machining process in a unit of a step in the numerical control system.
2. Description of the Prior Art
If the product dimensions in a drawing are highly precise, machining is conducted generally in the following steps (1) to (3);
(1) The first machining is conducted for a work by subtracting or adding a predetermined value from or to a preset tool offset value. The work which has been cut by the first machining process is of the size of a product plus a constant finishing stock. PA1 (2) Then, the dimension of the work which has been cut by the first machining is measured and the difference between the measured size and the product size is subtracted from or added to the tool offset value. PA1 (3) With the modified tool offset value, only the finishing step is repeated. PA1 where BLK (n): n means the number of blocks counted from the top block in the machining program. PA1 BLK (n1): the tool command block for the first machining step PA1 BLK (n2): the tool command block for the second machining step PA1 BLK (n3): the tool command block for the third machining step PA1 BLK (n4): the tool command block for the fourth machining step PA1 BLK (n5): the tool command block for the fifth machining step. PA1 The first machining step: BLK (n1) to BLK (n2-1) PA1 The second machining step: BLK (n2) to BLK (n3-1) PA1 The third machining step: BLK (n3) to BLK (n4-1) PA1 The fourth machining step: BLK (n4) to BLK (n5-1) PA1 The fifth machining step: BLK (n5) to . . . PA1 The first machining step: roughly cut outer diameter PA1 The second machining step: roughly cut inner diameter PA1 The third machining step: finishing outer diameter PA1 The fourth machining step: finishing inner diameter PA1 The fifth machining step: groove PA1 (1) A machining program 61 is displayed on the display screen 60. PA1 (2) The display is renewed until the desired block is displayed by means of a page key or the like. PA1 (3) The cursor 62 is moved to the desired block by means of a cursor key. PA1 The first machining step: roughly cut outer diameter PA1 The second machining step: roughly cut inner diameter PA1 The third machining step: finishing outer diameter PA1 The fourth machining step: finishing inner diameter PA1 The fifth machining step: groove,
When the machining is conducted according to the steps mentioned above, since the second machining concerns only the finishing step, the numerical control system has to be started midway of a machining.
As shown in FIG. 1, a machining program generally comprises of programs for each machining step which are arranged in the order of the machining. If it is assumed that the machining program for each machining step is a step program, and each block of the machining program is expressed as follows, then the machining program comprising five machining steps is regarded as step programs with blocks of BLK (n1), BLK (n2), BLK (n3), BLK (n4) and BLK (n5) arranged at the top of each step in the sequence of the machining order.
Since the machining step is defined by a tool to be used in the machining, the top block of each step program is a block designating a tool in which a tool change command 80 is written. Therefore, the top block of each step program becomes as follows;
The blocks included in the machining step become as follows;
It is now assumed that the following five machining steps are required to machine the work in accordance with the product dimensions designated in a drawing.
When the tool offset value is modified and the work is to be machined only for the finishing step, the machining for the second time is to start from the third step (or the step for the finishing outer diameter). In other words, the top block BLK (n3) of the third machining step is designated in the command as the midway starting block to start the machining.
For the method to designate a desired block (the top block of the machining program which the user wishes to execute) as the midway start block, FIG. 2 shows the display screen which indicates required operations as shown below:
If the machining program is executed under such conditions, it will start from the block (the block for midway start) at which the cursor 62 is positioned.
FIG. 3 is a block diagram to show an embodiment to realize a conventional midway start method. The conventional method will now be described referring to FIG. 3.
A machining program PRO to be executed is first stored in a machining program memory 4 in the form of a paper tape 1, a floppy disc 2, communication 3 and so on.
Then, the machining program PRO is read out from the machining program memory 4 and is displayed on a display unit 12 by means of a machining program display section 11. Since the number of blocks which can be displayed on the display unit 12 is limited as shown in FIG. 2, if it is assumed that the blocks BLK (n) through BLK (n+m-1) (wherein m means the number of blocks which can be displayed on the display unit 12) are currently displayed on the display unit 12, and if the key signal CSR sent out from an input unit 9 is a page-up key, the displayed screen is renewed so that the blocks BLK (n+m) through BLK (n+2m-1) will be displayed by means of the machining program display section 11. If the key signal CSR is a page-down key, the display screen will be renewed so that the blocks from BLK (n-m-1) to BLK (n-1) may be displayed on the screen.
In a case that the key signal CSR is for the cursor key, the cursor 62 shown in FIG. 2 is moved correspondingly to the key signal CSR and displayed on the screen. The key signal CSR is also sent out to a midway start block instruction section 10 from the input unit 9 so that the block (=midway start block) indicated by the cursor 62 which is displayed on the display unit 12 is specified based on the key signal CSR by the midway start block instruction section 10, and the number NCB of the blocks from the top block of the machining program to the midway start block is transmitted to a machining program executing section 5.
When a machining start command is inputted from an input unit (not shown), the machining program PRO is read in and interpreted in the unit of a block by means of the machining program executing section 5, and a motor control signal DTM and an I/O control signal DTS are respectively sent out to a motor controlling section 6 and an I/O controlling section 8. In a normal machining, the machining program PRO is read in from the top block BLK (1) by means of the machining program executing section 5, but reading-in will start from the midway start block BLK (NCB) if the number NCB of the blocks from the top to the midway start block is sent out from the midway start block instruction section 10.
A motor 7 comprising a feed shaft motor and a spindle motor or the like is driven by the motor controlling section 6 based on the motor control signal DTM sent out from the machining program executing section 5, and various driving systems are driven by the I/O controlling section 8 based on the I/O control signal DTS sent out from the machining program executing section 5.
In another executing method (sequence return), the machining program executing section 5 may interpret the machining program PRO from the top block BLK (1) to a block BLK (NCB-1) which is immediately preceding the midway start block without sending out the motor control signal DTM and the I/O control signal DTS, and send out the motor control signal DTM and the I/O control signal DTS from the midway start block BLK (NCB).
The conventional midway start method is problematic in the following points. If it is assumed that a machining program comprises the following step programs as shown in FIG. 1;
and if the machining program is to be started from the third machining step (for the finishing outer diameter), an operator must move the page key until the time the top block BLK (n3) of the third machining step is displayed, and further must manipulate the cursor key to move it to the top block BLK (n3) of the third machining step. Since the finishing step is usually positioned in the latter part of the machining program, the number of manipulations that the operator should have with keys such as the page key and the cursor key becomes enormous.
The conventional method is further defective in that it is extremely difficult to find a top block (or the tool command block related to the tool which is to be used in the machining step from which he/she wishes to start the machining program) of the machining step from which an operator wishes to start the program out of a large number of blocks displayed on the screen. Since such complicated operation becomes necessary every time he/she manipulates the page key, he/she has to bear a heavy burden and trouble.